Liquid developer containing extender body particles

ABSTRACT

Developed images with substantially no fogging in the background areas or streaking in the image areas are obtained in a liquid development system employing a liquid developer comprising an insulating liquid vehicle having dispersed therein charged toner particles and charged extender body pigment particles selected from the group consisting of calcium carbonate, aluminum hydroxide, barium sulfate, aluminum oxide, talc, silica, calcium silicate, magnesium carbonate, magnesium oxide and mixtures thereof.

United States Patent [191 Fukushima et a1.

LIQUID DEVELOPER CONTAINING EXTENDER BODY PARTICLES Filed: Nov. 13, 1972Appl. No.: 306,242

Related U.S. Application Data Continuation of Ser. No. 94,967, Dec. 3,1970, abandoned.

U.S. Cl. 252/62.l Int. Cl G03g 9/04 Field of Search 252/621; 106/15 FP;

References Cited UNITED STATES PATENTS 10/1942 Clayton et al. 117/1372/1948 Leatherman 106/15 FP 4/1952 Lauring 106/15 FP 3/1959 Mayer252/621 Nov. 26, 1974 2,899,335 8/1959 Straugham "252/621 3,031,3744/1962 Lowell 106/15 FP 3,079,270 2/1963 Cortez 252/621 3,244,633 5/1966Yellin et a1. 252/621 3,301,698 1/1967 Fauser et a1. 252/621 3,417,01912/1968 Beyer 252/621 FOREIGN PATENTS OR APPLICATIONS 1,016,072 l/1960Great Britain 252/621 Primary Examiner-Ronald H. Smith AssistantExaminer-J. P. Brammer [57] ABSTRACT Developed images with substantiallyno fogging in the background areas or streaking in the image areas areobtained in a liquid development system employing a liquid developercomprising an insulating liquid vehicle having dispersed therein chargedtoner particles andcharged extender body pigment particles selected fromthe group consisting of calcium carbonate, aluminum hydroxide, bariumsulfate, aluminum oxide, talc, silica, calcium silicate, magnesiumcarbonate, magnesium oxide and mixtures thereof.

6 Claims, N0 Drawings LIQUID DEVELOPER CONTAINING EXTENDER BODYPARTICLES This is a continuation of application Ser. No. 94,967, filedDec. 3, 1970, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to imaging systemsand more particularly to liquid development systems for developingelectrostatic latent images.

The formation and development of images on the surface of photoconductormaterial by electrostatic means is well known. The basicelectrostatographic process as taught by C. F. Carlson in U.S. Pat. No.2,297,691 involves placing a uniform electrostatic charge on aphotoconductive insulating layer exposing the layer to a light andshadow image to dissipate the charge on the areas of the layer exposedto the light and developing the resulting electrostatic latent image bydepositing on the image a finely divided electroscopic marking materialreferred to in the art as toner. The toner will normally be attracted tothose areas of the layer which retain a charge thereby forming a tonerimage corresponding to the electrostatic latent image. The powder imagemay then be transferred to a support surface such as paper andpermanently affixed to the support by any suitable means such as heatfixing or solvent fixing. Alternatively, the powder image may be fixedto the photoconductive layer if elimination of the powder transfer stepis desired. In addition, instead of latent image formation by uniformcharging and followed by imagewise exposure, the latent image may beformed by directly charging the layer in image configuration. Othermethods are known for applying electroscopic particles to the imagingsurface. Included within this group are the cascade developmenttechnique disclosed by E. N. Wise in U.S. Pat. No. 2,618,552; the powdercloud development technique disclosed by C. F. Carlson in U.S. Pat. No.2,221,776; and the magnetic brush process disclosed for example, in U.S.Pat. No. 2,874,063.

Development of an electrostatic latent image may also. be achieved withliquid rather than dry developer materials. In conventional liquiddevelopment, more commonly referred to as electrophoretic development,an insulating liquid vehicle having finely divided solid materialdispersed therein contacts the imaging surface in both charged anduncharged areas. Under the influence of the electric field associatedwith a charged image pattern the suspended particles migrate toward thecharged portions of the imaging surface separating out of the insulatingliquid. This electrophoretic migration of charged particles results inthe deposition of the charged particles on the imaging surface in imageconfiguration. Electrophoretic development of an electrostatic latentimage may, for example, be obtained by pouring the developer over theimage bearing surface, by immersing the imaging surface in a pool of thedeveloper or by presenting the liquid developer on a smooth surfaceroller'and moving the roller against the imaging surface. The liquiddevelopment technique has been shown to provide developed images ofexcellent quality and to provide particular advantages over otherdevelopment methods in offering ease in handling. Liquid developmentsystems also capable of providing high development speed, thedevelopment speed of commercial embodiments having recently reached alevel of ashigh as about 10 centimeters per second. However, with thecurrently available liquid development systems, this development speedis practical only for line copy since the development of continuous toneor halftone images generally requires a much slower speed.

The liquid developers generally employed in these electrophotographicimaging processes comprises fine electrically charged particlessuspended in an electrically insulating liquid. In addition to thecharged particles which are generally referred to as toner, it is commonto disperse or dissolve a charge controlling agent to regulate theelectric charge on toner particles and a dispersing agent to obtain astable dispersion.

A typical liquid developer employed in the production of black developedimages comprises carbon black particles suspended in a liquid such asthe highly insulating nonpolar organic solvents including mineral oil,benzene, heptane, cyclohexane and decylene. Typically, chargecontrolling agents including various resins, varnishes, nondrying oilsand wetting agents may be added to provide the necessary control ofcharge on the toner particles. While capable of forming satisfactoryimages, these liquid developers exhibit various shortcomings whenemployed in automatic machine configurations.

Specifically, difficulties are frequently encountered due to thephenomenon of fogging. Fogging occurs when, for example, aphotoconductive insulating layer is charged and exposed to a light andshadow pattern. In the background or nonimage areas, during exposure,light renders the photoconductive layer conductive and dissipates thecharge. However, in these background or nonimage areas when subjectingthe photoconductive insulating layer to even the strongest irradiation,a small electric charge persists in the nonimage or background areas.This small charge attracts a small amount of toner giving rise tofogging in the background areas of the developed print.

In addition, prior liquid developers may result in the formation ofstreaks on the image. Thus, when bringing an electrostatographic imagingsurface bearing an electrostatic latent image into contact with liquiddeveloper, a relative speed component is present between imaging surfaceand the liquid developer. Streaks are formed on the imaging surface inthe high density portions of the image along the direction of movementof developer relative to the imaging surface.

Furthermore, prior development systems employing a roller developerdispensing device, have resulted in the formation of apparatus stainsdue to the friction between the rollers and the surface holding theelectrostatic latent image. For example, in processes in which theliquid developer is supplied between the surface bearing theelectrostatic latent image and a metal roller which functions as thedeveloping electrode and is rolled across the imaging surface, or inimaging systems in which an electrophotographic material passes betweena pair of pinch rollers while the liquid developer is supplied betweenthe roller and the surface bearing the latent image staining of theapparatus may occur. This occurs since the metal rollers are kept indirect contact with the imaging surface, and any minute projectingportions present on the imaging surface are scraped by the metal rollerpermitting toner to be collected thereby forming stains.

Furthermore, the prior liquid developers are incapable of producingimage tone such as that obtainable in silver halide photographic paper.

SUMMARY OF THE INVENTION It is therefore an object of this invention toprovide a liquid development system which overcomes the above noteddeficiencies.

It is another object of this invention to provide a liquid developerwhich produces high density, nonstreaky developed images.

It is another object of this invention to provide a liquid developmentsystem which produces developed images with substantially no fogging.

It is another object of this invention to provide a liquid developmentsystem which is capable of producing fine grain smooth appearancedeveloped images.

It is another object of this invention to provide a liquid developmentsystem capable of producing developed images having a tone resemblingthe appearance obtained with silver halide photographic paper.

The above objects and others are accomplished, generally speaking, byproviding an electrostatographic imaging system of the liquiddevelopment type wherein a liquid developer comprising an insulatingliquid vehicle, charged colored particles and extender body pigmentparticles charged to the same polarity as the charged colored particlesis employed. In addition, if necessary, charge controlling agents,dispersion stabilizing agents, fixing agents and other well knownmaterials may be suspended or dissolved in the liquid developer.Alternatively, the charge control agents, the dispersion stabilizingagents and fixing agents may be coated on the individual chargedparticles.

Any suitable extender body pigment particle may be employed in thepractice of the present invention. By the term extender body pigment isintended to define that group of finely divided materials which willprovide a color the same as or similar to the background areas of thefinal print surface such as either a photosensitive paper such asElectrofax" paper or ordinary paper. In the most practical ofoperations, therefore, the body pigment particles will be substantiallywhite since most commercial imaging processes produce prints of blackimage areas on white background areas. It is, however, to be understoodthat if background areas of other colors are desired appropriatelycolored pigments of the background areas may also be employed.Typically, when employing body pigment particles in anelectrostatographic imaging system providing finished copy with whitebackground and dark color image areas, pigments with refractive indicesnot greater than 1.75 may be employed. Typical specific materialsinclude calcium carbonate, aluminum hydroxide, barium sulfate, aluminumoxide, talc, silica, calcium silicate, magnesium carbonate and magnesiumoxide. It is essential that the body pigment particles do not eitherdiscolor or decompose the tone particles.

The body pigment particles employed in the practice of the presentinvention may be of any suitable size. Typically, the body pigmentparticles are within the range of from several tens of times to severaltenths of the diameter of the color charged or toner particles. Toprovide uniformity of suspension in the liquid developer and deposition,it is preferred, however, to maintain the size of the body pigmentparticles within a range of several times larger to several timessmaller than the toner particles. Typically, the extender pigment is ofa particle size of from about 0.01 to about 5 microns. The tonersemployed in the practice of this invention may be of any suitable size.Typically, the toner particles do not have an average particle sizeexceeding about 1 micron or less than about 0.01 micron. Thus, theextender body pigment particles will generally be of about the same sizeas toner particles. Generally the number of extender body pigmentparticles may be employed in an amount within the range of from aboutone tenth to about ten times the amount of the charged toner particlespresent in the liquid developer. However, to avoid the deposition ofundue quantities of extender body pigment particles in the image areas,it is generally preferred that the extender body pigment particles bepresent in an amount within the range of from about one quarter to abouttwice the amount of the charged toner particles. Optimum image densityin the image areas together with substantially complete reduction offogging in the nonimage or background areas, it is generally achievedwhen the number of extender body pigment particles is about the sameamount as that of the charged toner particle.

The liquid developer of the present invention may be prepared in anysuitable manner. Typically, the liquid developer may be prepared bymixing the several constituents of the developer together. It may alsobe prepared by mixing a first liquid portion containing the tonerparticles with an insulating liquid and a second portion containing thebody pigment particles. Alternatively, a paste containing toner and bodypigment particles may be dispersed within the insulating liquid.

From the above description of the invention, the choice of specificmaterials and operating conditions is deemed to be well within the scopeof those skilled in the art and therefore the scope of the invention isnot limited by the hereinabove mentioned illustrative materials. Theextender body pigment particles may be employed with any suitable liquiddeveloper. Typical liquid developers contain liquids of relatively highinsulating value generally having a volume resistivity greater thanabout 10 ohm-cm so as not to effect the electrostatic charge pattern onthe insulating layer and low dielectric constants of less than about3.4. Typical specific vehicles include hydrocarbons such as benzene,xylene, hexane, naptha, kerosene, halogenated hydrocarbons such ascarbon tetrachloride, trichloroethylene and chloroform. Typical chargedtoner particles which may be employed with the liquid developer include,among others, charcoal, carbon black, magnesium oxide, lithopone,cadmium yellow, chrome yellow, cobalt blue, cadmium red, burnt siena,Hansa yellow, rose bengal and phthalocyanine. Typically, the chargedtoner particles are present in the liquid developer in an amount of fromabout 2 to about 20 grams per liter, and are conventionally dispersedand suspended in the liquid by stirring or agitation. Where a highlyuniform stable suspension is desired, this suspension may be passedthrough a colloid mill. The liquid developers according to the presentinvention may be employed to develop electrostatic charge patternspresent on any suitable imaging surface. Basically, any material capableof holding a charge pattern may be employed. Typical materials includedielectric layers, xeroprinting masters and photoconductors. Aparticularly preferred material for use in automatic copying machines isa photosensitive paper comprising photoconductive pigment particles inan insulating binding layer. Typically, this paper comprises zinc oxidephotoconductive particles present in an insulating binding layer whichis overcoated on a paper substrate. The choice of particular imagingmember and particular development technique may be readily determined byone skilled in the art. For example, the photosensitive paper describedabove may be substituted with photoconductor materials made from cadmiumsulfide, zinc sulfide, Zinc selenide, cadmium selenide, titaniumdioxide, phthalocyanine and polyvinyl carbazole. As previouslydiscussed, the liquid developers according to the present invention mayalso contain dispersed in the insulating liquid vehicle charge controlagents and suspending agents for their well known functions. Theselection of the appropriate materials to perform these well knownfunctions may be readily made by the artisan.

When employing a liquid developer comprising toner particles which arepositively charged, the extender body pigment particles must also bepositively charged in the insulating liquid. The use of calciumcarbonate and aluminum hydroxide as the extender body pigment particlesis particularly preferred when positively charged particles are to beemployed since they become positively charged merely be being suspendedin the insulating liquid. In order to disperse these minute particles toprovide a stable suspension in the insulating liquid a resin may also beemployed. Typically, from about 0.5 to about 50 parts by weight of theresin per part of the extender pigment may be employed. A portion ofthis resin appears to be strongly absorbed on the surface of the calciumcarbonate or the aluminum hy droxide and the charge on these particlesmay be further stabilized depending on the specific resin employed.Typically, from about 2% to about 30% by weight of the total resin isabsorbed on the surface of the extender pigment. A particularlypreferred resin providing maximum stabilization of charge and suspensionis a rosin modified phenol formaldehyde resin heated with linseed oil.

While the above explanation has been made principally with regard totoner particles carrying a positive charge, it is to be understood thatthe present invention also encompasses liquid developers containingtoner particles which have been provided with a negative charge. Liquiddevelopers containing negatively charged toner particles may be employedto develop positively charged image patterns. They may also be used asreversal developers. In both instances, the liquid developers may haveextender body pigments added which are capable of being negativelycharged. It has been observed that the liquid developer will exhibit thebehavior of a negative toner when the amount of negatively charged tonerparticles present in the liquid developer is larger than that of thepositively charged body pigment particles. Conversely, the developerwill exhibit the behavior of a positive toner when the amount ofpositively charged extender pigment is greater than the negativelycharged toner particles. This occurs since the negatively charged tonerparticles are encircled by the extender particles so the toner particlesbehave as positive toners.

It is possible to maintain the negative polarity charge of the liquiddeveloper by the use of a charge controlling agent. Any suitable chargecontrolling agent may be employed. A typical material for controllingthe charge is lecitin. It is also possible to provide the body employedas an electrophoretic liquid developer is capable of producing imageswhich are essentially, completely free from background fogging. Inaddition, the developer of this invention provides images of clear toneresembling the appearance of silver halide photographic paper.Furthermore, the liquid developer according to this invention, providesa very fine grain developed toner image. In addition, the absence ofstain resulting from friction between the developer applicator rollerand the imaging surface wherein a roller developing method is employedis substantially completely eliminated. i

While the exact mechanism and. reasons for the improved results are notfully understood at the current time, it is presently believed that thedevelopment of images which are substantially free from backgroundfogging is due to a preferential deposition of the extender body pigmentin the background portions of the imaging surface which thereby preventdeposition and adherence of the toner in these background portions. Itis further believed that the clear tone resembling the appearance ofsilver halide reproductions is due to the fact that the extender bodypigment particles and the toner particles are deposited together andthereby increase the transparency of the toner image. The fact thatfiner grain toner images are capable of being achieved with the liquiddeveloper of the present invention is believed attributable to the factthat aggregates which consist exclusively of a toner material areprevented since there is a simultaneous deposition of toner and extenderpigment in the image areas which tends to suppress the formation oflarge aggregates which consist solely of colored toner material. Theabsence of staining is further believed to be attributed to the factthat the body pigment particles act as a lubricant or to thepreferential deposition of the body pigment particles on the projectingportions of the imaging surface. The ability to produce images which aresubstantially free from streaks in a liquid development system ofincreased development speed has not been satisfactorily explained. Ithas been established, however, that with comparison of liquid developeraccording to the present invention and developers containing resinparticles instead of extender body particles that increased developmentspeed and the above mentioned improved image qualities are achieved.

DESCRIPTION OF PREFERRED EMBODIMENTS The following, nonlimiting examplesfurther define, describe and compare preferred materials, methods andtechniques of the present invention. Example ll is presented forcomparative purposes. Unless otherwise specified, all amountsproportions and percentages are by weight.

EXAMPLE I A photosensitive paper comprising an electroconductive papersubstrate overcoated with a photoconductive layer of powdered zinc oxidein an insulating resinous binder is charged and exposed to a light andshadow pattern in conventional manner. The electrostatic latent imageformed on the zinc oxide sheet is developed by passing the sheet througha bath of a liquid developer made according to the following procedure:

Paste A is obtained by ball milling the following composition for 8hours.

Carbon black 4000g (particle size 0.05 added Varnish obtained by heatinga mixture of SOOOg equal amounts of rosin-modified phenolformaldehyderesin and linseed oil Linseed oil lOOOg Paste B is obtained by kneadingthe following composition on a three roll kneader.

Aluminum hydroxide 2000g (particle size 0.07 0.2a)

Varnish obtained by heating a mixture of 4000g rosin-modifiedphenol-formaldehyde resin and linseed oil Linseed oil IOOOg Theprocedure of Example I is repeated except that only 20 grams of paste Ais dispersed in 10 liters of Decalin. The developed image on zinc oxidepaper has a high fogging level, streaky images and a relatively coarsegrain image. In addition, the tone is inferior to that obtained in thesilver halide photographic paper.

EXAMPLE III The procedure of Example I is repeated except that theliquid developer is made by dispersing 20 grams of paste A in 5 litersof Decalin" and grams of paste !B in 5 liters of Decalin". When mixedtogether in equal amounts a liquid developer is formed which when iemployed to develop an electrostatic latent image formed in the mannerdescribed in Example I produces Q prints of quality similar to thatobtained in Example I.

l I g 7 EXAMPLE IV The procedure of Example I is repeated except thatdevelopment of the electrostatic latent image is accomplished with aliquid developer made by blending the following composition in a ballmill for one hour.

Phthalocyanine blue 400g Polymerized linseed oil 500g Linseedoil-modified alkyd resin 500g Aluminum hydroxide 200g Kerosene 300mlForty grams of this paste is then dispersed in 10 liters of kerosenewhile under the influence of ultrasonic wave. The toner has a stablepositive charge in the carrier liquid. When used as a liquid developer,in the manner described in Example I, an image with substantially nofogging or streaking is obtained. In addition, the image is moretransparent than that obtained by means of ordinary electrophotographicprocessing.

EXAMPLE V The procedure of Example I is repeated with a liquid developerprepared by blending the following composition in a ball mill for onehour in the following manner.

Brilliant carmine 6B 250g Polymerized linseed oil 250g Linseedoil-modified alkyd resin 300g Precipitated barium sulfate 200g Kerosene300ml Thirty grams of this paste are dispersed while under the influenceof ultrasonic wave into a mixture of 8 liters of cyclohexane and 2liters of kerosene to provide a liquid developer capable of providing ared image. The precipitated barium sulfate is provided with positivecharge in the carrier liquid. Image quality similar to that described inExample IV is achieved.

EXAMPLE VI The procedure of Example I is repeated with the liquiddeveloper prepared by blending the following composition in a ball millfor one hour.

Benzidine yellow 40g Varnish (same as in Example I) g Linseed oil 60gAluminum hydroxide l5g Calcium carbonate l5g Twenty grams of this pasteare dispersed while under the influence of ultrasonic wave into amixture of 8 liters of cyclohexane and 2 liters of kerosene. Theparticles of benzidine yellow when employed alone exhibit an unstablepositive charge in the carrier liquid. Calcium carbonate shows strongpositive charge in the carrier liquid and stabilized the positive chargeon the benzidine yellow. Image quality similar to that achieved inExample IV is observed when the zinc oxide sheet is immersed in theliquid developer.

EXAMPLE VII A photoconductive insulating layer comprising a papersubstrate with a coating thereon of zinc oxide photoconductive particlesin an insulating resinous binder is charged and exposed to a negativeimage. Theelectrostatic latent image thus formed is developed with aliquid developer prepared by blending the following composition in aball mill.

Calcium carbonate 250g Vinyl chloride-vinyl acetate copolymer 125gVarnish obtained by heating rosin-modified phenol-formaldehyde resin andlinseed oil 400g Ethyl acetate 3000m| Thirty milliliters of the paste isdispersed while under the influence of ultrasonic wave in a carrierliquid of the following composition.

Cyclohexane l500ml Kerosene 300ml Cottonseed oil 200ml This developercontains negatively charged particles and is substantially transparentin appearance.

A developer containing negatively charged green toner of the followingcomposition is prepared in the same manner.

Phthalocyanine green g Polymerized linseed oil g Cyclohexane l500mlKerosene 475ml of the present invention. There are other systems andtechniques which may be substituted for those described. Othermodifications of the present invention will occur to those skilled inthe art upon a reading of the present disclosure which modifications areintended to be included within the scope of this invention.

We claim:

1. An electrostatographic liquid developer comprising an insulatingliquid vehicle having a volume resistivity greater than about 10 ohm-cmand dispersed therein charged colored toner particles and white extenderbody pigment particles selected from the group consisting of calciumcarbonate, aluminum hydroxide, and mixtures thereof; said extender bodypigment particles being present in from about one tenth to about tentimes the amount of the charged colored toner particles and having aparticle size of from about 0.01 to about 5 microns, said tonerparticles having a size of from about 0.01 to about 1 micron; saidextender body pigment particles having a positive charge, both saidcharged toner particles and said charged body pigment particles beingcapable of being simultaneously deposited from said liquid developer inresponse to a charge of opposite polarity on the latent image areas ofan imaging surface and said charged body pigment particles being capableof preferential deposition in the background portions of said imagingsurface.

2. The liquid developer of claim 1 wherein said extender body pigmentparticles are present in from about one quarter to twice the amount ofthe charged toner particles.

3. The liquid developer according to claim 1 wherein said body pigmentparticles are calcium carbonate.

4. The liquid developer according to claim 1 wherein said body pigmentparticles are aluminum hydroxide.

5. The liquid developer of claim 1 wherein said extender body pigmentparticles have a refractive index less than about 1.75.

6. The liquid developer of claim 1 wherein said extender body pigmentparticles have a charge and suspension stabilizing resin absorbed on thesurface.

1. AN ELECTROSTATORGRAPHIC LIQUID DEVELOPER COMPRISING AN INSULATINGLIQUID VEHICLE HAVING A VOLUME RESISTIVITY GREATER THAN ABOUT 10**10OHM-CM AND DISPERSED THEREIN CHARGED COLORED TONER PARTICLES AND WHILEEXTENDER BODY PIGMENT PARTICLES SELECTED FROM THE GROUP CONSISTING OFCALCIUM CARBONATE, ALUMINUM HYDROXIDE, AND MIXTURES THEREOF; SAIDEXTENDER BODY PIGMENT PARTICLES BEING PRESENT IN FROM ABOUT ONE TENTH TOABOUT TEN TIMES THE AMOUNT OF THE CHARGED COLORED TONER PARTICLES ANDHAVING A PARTICLE SIZE OF FROM ABOUT 0.01 TO ABOUT MICRONS, SAID TONERPARTICLES HAVING A SIZE OF FROM ABOUT 0.01 TO ABOUT 1 MICRON; SAIDEXTENDER BODY PIGMENT PARTICLES HAVING A POSITIVE CHARGE, BOTH SAIDCHARGED TONER PARTICLES AND SAID CHARGED BODY PIGMENT PARTICLES BEINGCAPABLE OF BEING SIMULTANEOUSLY DEPOSITED FROM SAID LIQUID DEVELOPER INRESPONSE TO A CHARGE OF OPPOSITE POLARITY ON THE LATENT IMAGE AREAS OFAN IMAGING SURFACE AND SAID CHARGED BODY PIGMENT PARTICLES BEING CAPABLEOF PREFERENTIAL DEPOSITION IN THE BACKGROUND PORTIONS OF SAID IMAGINGSYRFACE.
 2. The liquid developer of claim 1 wherein said extender bodypigment particles are present in from about one quarter to twice theamount of the charged toner particles.
 3. The liquid developer accordingto claim 1 wherein said body pigment particles are calcium carbonate. 4.The liquid developer according to claim 1 wherein said body pigmentparticles are aluminum hydroxide.
 5. The liquid developer of claim 1wherein said extender body pigment particles have a refractive indexless than about 1.75.
 6. The liquid developer of claim 1 wherein saidextender body pigment particles have a charge and suspension stabilizingresin absorbed on the surface.